1. Field of the Invention
The present invention relates to a catalytic converter for purification of exhaust gas emitted from an automotive engine.
2. Description of the Prior Art
An example of a catalytic converter of this kind is disclosed by Japanese Provisional Patent Publication No. 54-13462 and also shown in FIGS. 7A to 7E.
Referring to FIGS. 7A to 7E, the catalytic converter consists of a flat thin sheet of metal 1 (FIG. 7D) and a corrugated thin sheet of metal 2 overlapping each other and wound into a spiral shape to form a honeycomb-like body. The honeycomb-like body is inserted into a shell 3, and thereafter the sheets 1 and 2 and the shell 3 are soldered together to constitute a monolithic catalytic element which is then coated with a precious metal serving as a catalyst.
The shell 3 of the catalytic element is welded at opposite ends to diffusers 4 and 4 welded to flanges 5 and 5 for attachment to exhaust pipes (not shown), respectively.
In use, the shell 3 is subjected to atmospheric cooling and therefore maintained at a relatively low temperature (about 400.degree. C.) whilst on the contrary the honeycomb monolith 6 constituted by the flat and corrugated sheets 1 and 2 is heated up to a high temperature (about 800.degree. C.) by the hot exhaust gases passing therethrough and further by the heat generated by the catalyst covering the outer surface thereof. Due to this, a thermal expansion differential is caused between the shell 3 and the honeycomb monolith 6, and as shown in FIG. 7(E) the honeycomb monolith 6 is expanded or extended relative to the shell 3 in the longitudinal direction of the passages through which the exhaust gases flow, causing a problem that the soldered joint between the shell 3 and the honeycomb monolith 6 is broken to allow both to be separated from each other and cause play, rattling sounds and, in the worst case, breakage thereof.